497 



broad. Last pair of uropoda projecting beyond the others, rarai spinous 

 and setiferous, the outer one generally much the larger, and having a small 

 terminal joint. Telson rather small, and cleft to the base. 



Remarks. In the restriction now generally adopted, this genus is 

 chiefly distinguished by the slender, compressed body (the back of which is 

 generally evenly rounded), by the peculiar spinulose armature of the urosome, 

 by the slender antennae, and by the structure of the last pair of uropoda, and 

 telson. The species are rather numerous and widely distributed, inhabiting 

 both salt and fresh water. The marine forms are chiefly littoral or sub- 

 littoral in their occurrence. To the fauna of Norway belong 5 species (to be 

 discribed below), one of which is a true fresh-water form. 



8. Gammarus marinus. Leach. 



(PI. 175.] 

 Gammarus marinus, Leach, Lin. Trans. XI, p. 352. 



Syn.: Gammarus Olivii, M.-Echv. 



poecilurus, Eathke. 

 Kroyeri, Rathke. 



Body slender and compressed, with the back evenly rounded 

 throughout. Cephalon scarcely as long as the first 2 segments of 

 mesosome combined, lateral corners transversely truncated at the tip, and 

 defined below by a rather deep emargination filled up by the greatly 

 swollen basal joint of the inferior antennae. Anterior pairs of coxal plates 

 not nearly twice as deep as the corresponding segments; 4th pair scarcely 

 as broad as they are deep, and having the posterior expansion obliquely 

 truncated. Last pair of epimeral plates of metasome but little produced at 

 the lateral corners. Segments of urosome without any dorsal projections, 

 but each provided with 2 above-converging, transverse rows of strong spinules, 

 each row containing from 6 to 9 spinules arranged in 2 groups slightly apart. 

 Eyes very narrow, oblong reniform, occupying nearly the entire height of the 

 front part of the head, pigment very dark. Superior antennas nearly half 

 the length of the body, 1st joint of the peduncle equalling in length the 

 other 2 combined; flagellum more than twice the length of the peduncle, and 

 composed of about 33 articulations; accessory appendage not quite half as 

 long as the peduncle, and very slender, being composed of about 7 articula- 

 tions. Inferior antennae considerably shorter than the superior, and having 

 the flagellum somewhat longer than the peduncle. Gnathopoda not very 



05 Crustacea. 



